The present invention relates to a toner for developing an electrostatic latent image formed on a latent-image carrier and to an image forming apparatus for forming an image using this toner.
More particularly, the present invention relates to a non-magnetic mono-component toner to be used for developing an image according to a non-magnetic mono-component developing method using a conductive developing roller and to an image forming apparatus using the non-magnetic mono-component toner.
Further, the present invention relates to a toner in which additive particles are entrapped in mother particles and to an image forming apparatus using this toner.
Among conventional known image forming apparatuses, there is a multicolor image forming apparatus of intermediate transfer type as shown in FIG. 1. In an image forming apparatus 1 of this type, an image is exposed to light as an electrostatic latent image onto a photoreceptor 2 as a latent image carrier. The electrostatic latent image on the photoreceptor 2 is developed by yellow, magenta, cyan, and black non-magnetic mono-component developing devices 3, 4, 5, 6 in this order (the order of respective colors is arbitrary) so as to obtain visible developed images. The developed images on the photoreceptor are superposed and toned on an intermediate transfer belt 7a of an intermediate transfer member 7, thus achieving primary transfer. After the primary transfer, the toned image is transferred to a recording media 9 such as a paper on a secondary transfer roller 8a of the transferring device 8, thus achieving secondary transfer. After that, the image is heated and fixed to the recording media 9 by a fixing device 10, thereby obtaining a desired image on the recording media 9.
The respective non-magnetic mono-component developing devices 3, 4, 5, 6 have substantially the same structure. That is, each of the developing devices 3, 4, 5, 6 is of a contact developing type that a conductive developing roller 16 is arranged in contact with the photoreceptor 2. As shown in FIG. 2(a), non-magnetic mono-component toner particles T in a toner container 13 are carried by a toner carrying means 14 to a toner supply roller 15 as toner supply means and is further supplied to the developing roller 16 by the toner supply roller 15. Accordingly, the non-magnetic mono-component toner particles T are held on the surface of the developing roller 16. A bias voltage composed of an alternating current superimposed on a direct current is applied to the developing roller 16 and the, developing roller 16 is rotated at a high speed, whereby the non-magnetic mono-component toner particles T are regulated to be in a uniform thin layer by a toner regulating member 17 as toner regulating means, which is in press contact with the surface of the developing roller 16, and are uniformly charged. After that, the non-magnetic mono-component toner particles T on the developing roller 16 are uniformly conveyed toward the photoreceptor 2 which is in contact with the developing roller 16.
The non-magnetic mono-component toner particles T on the developing roller 16 is transferred to the photoreceptor 2 by developing voltage applied to the developing roller 16, whereby an electrostatic latent image is developed with the non-magnetic mono-component toner particles T on the photoreceptor 2.
The non-magnetic mono-component developing method employing conductive developing roller 16 also includes a non-contact developing method in which the developing roller 16 and a photoreceptor 2 are spaced apart from each other. In developing of the non-contact developing method, a developing voltage is applied to the developing roller 16 and non-magnetic mono-component toner particles T on the developing roller 16 is transferred by jumping to the photoreceptor 2 due to the developing voltage. That is, an electrostatic latent image on the photoreceptor 2 is developed with the non-magnetic mono-component toner particles T by jumping-developing.
By the way, in the non-magnetic mono-component developing method using such a conductive developing roller 16, both cases of the non-contact development or contact development, an image force Fm acts between the non-magnetic mono-component toner particles T and the developing roller 16 as shown in FIG. 3. To securely separate the non-magnetic mono-component toner particles T from the developing roller 16 and to transfer the toner particles T to the photoreceptor 2, a coulomb force Fc capable of overcoming the image force Fm should be imparted to the non-mono-component toner particles T. Since the coulomb force Fc imparted to the non-magnetic mono-component toner particles T increases as the image force Fm increases, the developing voltage should be accordingly increased. However, too large developing voltage must cause discharge. Therefore, the developing voltage can not be increased so large. This means that the developing bias has an upper limitation. There is accordingly a problem of narrow margin for developing.
As the image force Fm is large, the effect of removing residual toner particles remaining on the developing roller 16 after developing by the toner supply roller 15 is reduced, thus facilitating producing undesirable developing hysteresis. That is, when the image force Fm is not so large, residual toner particles remaining on the developing roller 16 can be peeled off by the toner supply roller 15 as shown in FIG. 4(a). Therefore, the residual toner particles do not pass through spaces between the developing roller 16 and the toner supply roller 15 and thus does not move to the toner regulating means 17 side. Therefore, toner particles on the developing roller 16 between the toner supply roller 15 and the toner regulating means 17 are new non-magnetic mono-component toner particles T supplied from the toner supply roller 15 only.
On the other hand, when the image force Fm is so large, the residual toner particles can not be completely peeled off by the toner supply roller 15 as shown in FIG. 4(b). Therefore, some of the residual toner particles pass through spaces between the developing roller 16 and the toner supply roller 15 and thus move to the toner regulating means 17 side. Since no non-magnetic mono-component toner particle T is newly supplied from the toner supply roller 15 to portions, to which residual toner particles adhere, of the developing roller 16, the residual toner particles are carried as developer and are further charged by passing through the toner regulating means 17 so as to have larger charge. Difference in charge leads to difference in image density between a portion developed with the residual toner particles and a portion developed with new non-magnetic mono-component toner particles. That is, undesirable developing hysteresis appears.
After a solid image is printed, the amount of residual toner particles is reduced and the influence of the image force Fm is thus reduced, so none of the residual toner particles passes through spaces between the developing roller 16 and the toner supply roller 15. Therefore, non-charged new non-magnetic mono-component toner particles T, which are not charged yet, are supplied to the developing roller 16 from the toner supply roller 15 so that the non-magnetic mono-component toner particles T are suitably charged by the toner regulating means 17. However, after a white solid image is printed, the amount of residual toner particles is increased because most of the non-magnetic mono-component toner particles T are not developed, so the influence of the image force Fm is thus increased. As the image force Fm is large, some of the residual toner particles pass through spaces between the developing roller 16 and the toner supply roller 15. The residual toner particles are further charged by passing through the toner regulating means 17 so as to have larger charge. The charge of non-magnetic mono-component toner particles differs due to what type of image printed by just the last circle of the developing roller 16, particularly, solid image or white solid image. Therefore, even when printing the same pattern, density unevenness appears. That is, undesirable developing hysteresis appears.
On the other hand, a toner T conventionally used contains additive particles which are dispersed in mother particles in order to improve the characteristics of the toner or to facilitate the preparation of the toner.
For example, to stabilize the electric characteristic of the toner, a charge controlling agent called as xe2x80x9cCCAxe2x80x9d is dispersed as an additive in mother particles. To impart manifestation of color and/or permeability to the toner, a pigment is entrapped and dispersed as an additive in mother particles.
Further, the conventional toners are prepared by a pulverization method or polymerization method. In toners prepared by pulverization, a mold releasing agent and/or a pulverization assisting agent are kneaded with mother particles of the toner. In toners prepared by polymerization, a polymerization reaction assisting agent such as an initiator or dispersant is used as an additive for polymerization reaction.
However, some particles of such additives entrapped in mother particles of the toner may be liberated from the mother particles to become liberated additive particles. The liberated additive particles may affect the carrying property and charging property of the toner because the liberated additive particles adhere to the surface of a processing member such as the developing roller of the developing device.
For example, some particles of a CCA do not enter into mother particles during preparation of the toner so as to form liberated CCA particles liberated from the mother particles. On the other hand, the surface of the developing roller may be exposed at locations where a large amount of toner particles is consumed. As the surface of the developing roller is exposed, when new toner is supplied to the developing roller, the liberated CCA particles in the new toner adhere to the exposed surface of the developing roller. Since the liberated CCA particles have a particle diameter smaller than that of the mother particles and have a charging property stronger than that of the mother particles, once the liberated CCA particles adhere to the surface of the developing roller, the CCA particles are hardly separated from the developing roller because of image forces and intermolecular forces therebetween. Moreover, the adhering force between the liberated CCA particles and the developing roller is increased by friction created by the toner regulating member and the like.
As many liberated CCA particles adhere to the developing roller, there are differences in carrying characteristic and charging characteristic of the toner between a portion where many liberated CCA particles adhere and a portion where little liberated CCA particles adhere. There are differences in amount of toner developed on the photoreceptor between the aforementioned portions. As a result, a band-shaped unevenness of density appears on the resultant image. The adherence of the liberated CCA also shortens the lifetime of the developing device.
Therefore, it is desired to prevent liberated CCA particles from adhering to processing members such as the developing roller.
As another example, parts of pigment do not enter into mother particles during preparation of the toner so as to form pigment liberated from the mother particles. A portion of the resultant image corresponding to portion where the liberated pigment adheres to a processing member such as the developing roller should be white blank.
Further, the liberated pigment particles have a diameter larger than the pigment particles dispersed in the mother particles. Pigment functions xe2x80x9cto impart manifestation of colorxe2x80x9d and xe2x80x9cto impart permeability to a tonerxe2x80x9d when dispersed as micro particles in mother particles of resin. When the ratio of liberated pigment relative to entire pigment is high, the manifestation of color and the permeability may be affected. That is, poor manifestation of color leads to insufficient density and poor permeability leads to poor permeability of OHP.
Therefore, it is desired to prevent liberated pigment from adhering to the developing roller and other processing members.
Further in toners T prepared by pulverization, metallic soap is frequently kneaded as additives such as a mold releasing agent and a pulverization assisting agent together. Poor dispersion of the metallic soap leads to liberation of metallic soap particles from the mother particles. As the liberated metallic soap particles adhere to a processing member such as the developing roller, image defects such as image blurs may be produced.
Therefore, it is desired to prevent liberated metallic soap particles from adhering to processing members such as the developing roller.
Furthermore, in toners prepared by polymerization such as emulsion polymerization, a polymerization reaction assisting agent as an additive such as an initiator or dispersant may not be completely used in polymerization reaction, so a part of the polymerization reaction assisting agent not used becomes residue after dehydrating and drying processes. The residual polymerization reaction assisting agent may exist in the state liberated from the mother particles in the toner particles. The liberated polymerization reaction assisting agent facilitates coagulation of toner and thus provides poor fluidity of toner. Therefore, a predetermined carrying rate may not be obtained.
Therefore, it is desired to improve the fluidity of polymerized toner.
It is an object of the present invention to provide a non-magnetic mono-component toner which allows lower developing voltage and can achieve reduction in developing hysteresis and to provide an image forming apparatus employing the non-magnetic mono-component toner.
It is another object of the present invention to provide a toner which can further inhibit the influence of liberated additive particles even when additives are added in the mother particles and to provide an image forming apparatus employing the toner.
To achieve the aforementioned object, a non-magnetic mono-component toner of the present invention comprises, at least, a plurality of mother particles and a plurality of CCA particles which are attached to the mother particles, and is characterized by satisfying the following equation:
axc3x97d less than 2.5
wherein xe2x80x9caxe2x80x9d is the inclination of an approximation straight line of said CCA particles adhering to said mother particles, obtained by approximating distribution of particle diameter of said CCA particles relative to the particle diameter of said mother particles by the least-square method, and xe2x80x9cdxe2x80x9d (xcexcm) is the volume-based mean particle diameter of said toner.
The non-magnetic mono-component toner of the present invention is characterized in that the amount of said mother particles to which no CCA particle adheres is 3.0% or less of the entire toner.
Further, the non-magnetic mono-component toner of the present invention is characterized by satisfying the following equation:
axc3x97dxe2x89xa71.0
An image forming apparatus of the present invention comprises: a latent image carrier on which an electrostatic latent image is formed; and a developing device having a conductive developing roller for carrying a non-magnetic mono-component toner to develop the electrostatic latent image on said latent image carrier, a toner supply means for supplying said non-magnetic mono-component toner to said conductive developing roller, and a toner regulating means for regulating the non-magnetic mono-component toner to be carried toward said latent image carrier and charging said non-magnetic mono-component toner, and is characterized in that said non-magnetic mono-component toner is the aforementioned non-magnetic mono-component toner of the present invention.
Further, a toner of the present invention comprises, at least, a plurality of mother particles and a plurality of additives which are added to the mother particles, and is characterized by that the liberation ratio of liberated additives liberated from said mother particles is set to be equal to or less than a specified value corresponding to the additives.
The toner of the present invention is characterized in that a CCA is used as one of said additives and the liberation ratio of the liberated CCA is set to be 1.0% or less.
Further, the toner of the present invention is characterized in that a pigment is used as one of said additives and the liberation ratio of the liberated pigment is set to be 0.6% or less.
Furthermore, the toner is a pulverized toner prepared by pulverization, and that at least one of a mold releasing agent and a pulverization assisting agent is used as one of said additives and the liberation ratio of the at least one of the mold releasing agent and the pulverization assisting agent liberated from the mother particles is set to be 0.4% or less.
Moreover, the toner of the present invention is characterized in that the toner is a polymerized toner prepared by polymerization, and that at least one of an initiator and a dispersant to be added for polymerization reaction is used as one of said additives and the liberation ratio of the at least one of the initiator and the dispersant from the mother particles is 0.3% or less.
An image forming apparatus of the present invention comprises: a latent image carrier on which an electrostatic latent image is formed; and a developing device having a conductive developing roller for carrying a toner to develop the electrostatic latent image on said latent image carrier, and a toner regulating means for regulating the toner to be carried toward said latent image carrier and charging said toner, and is characterized in that said toner is the aforementioned toner of the present invention.
In the non-magnetic mono-component toner T of the present invention having the aforementioned structure, the inclination xe2x80x9caxe2x80x9d of the CCA adhering to mother particles is relatively gentle, so the concentration of the CCA is relatively low. Therefore, when the non-magnetic mono-component toner is charged by passing through the toner regulating means of the developing device, the charge of one particle of the non-magnetic mono-component toner is relatively small. In addition, the mean particle diameter xe2x80x9cdxe2x80x9d of the non-magnetic mono-component toner T is also relatively small so that the amount of the CCA in one particle of the non-magnetic mono-component toner, composed of one mother particle and CCA adhering to the mother particle, can be small. Similarly, the charge on one particle of the non-magnetic mono-component toner can be also small. By setting the inclination xe2x80x9caxe2x80x9d of the CCA adhering to the mother particles and the mean particle diameter xe2x80x9cdxe2x80x9d of the non-magnetic mono-component toner T to satisfy the equation axc3x97d less than 2.5, the charge on one particle of the non-magnetic mono-component toner can be efficiently reduced.
Particularly, according to the non-magnetic mono-component toner of the present invention, the amount of mother particles to which no CCA particle adheres or the amount of the asynchronous toner is set to be 3.0% or less of the entire non-magnetic mono-component toner, whereby the amount of defective charged toner particles, which are charged in the opposite polarity, can be reduced.
Further, according to the non-magnetic mono-component toner of the present invention, the aforementioned xe2x80x9caxc3x97dxe2x80x9d is set to be 1.0 or more, whereby somewhat large image force can be ensured. The larger the image force is, the larger the toner carrying force is, thereby preventing toner leakage.
On the other hand, according to the image forming apparatus using the non-magnetic mono-component toner of the present invention, because the charge of one particle of the non-magnetic mono-component toner can be reduced, the image force acting between the particles of the non-magnetic mono-component toner and the developing roller can be also reduced. This allows the coulomb force Fc required for developing to be small, thus allowing the developing voltage to be small. Accordingly, in the contact developing method or the non-contact jumping developing method, a margin relative to a discharge starting voltage can be effectively obtained. Particularly, in the developing method using a bias voltage composed of AC superimposed on DC, an enough margin can be obtained.
In addition, because the image force of the non-magnetic mono-component toner is small, residual toner particles remaining on the developing roller after developing can be easily peeled off by the toner supply roller, thereby further ensuring the collection of the residual toner particles. Therefore, supplied to the developing roller between the toner regulating means and the toner supply means are new non-magnetic mono-component toner particles only, thereby reducing the developing hysteresis and also reducing the charge of the non-magnetic mono-component toner after passing through the toner regulating means.
In the toner of the present invention, the liberation ratio of librated additive is set to be equal to or less than a specified value corresponding to the additive, thereby restraining the amount of liberated additive liberated from mother particles Therefore, the probability of contact of liberated additive particles with the surfaces of processing members including the developing roller is small, thereby reducing the influence of the liberated additive on the carrying property and charging property of the toner.
Particularly, according to the toner of the present invention, the liberation ratio xe2x80x9chxe2x80x9d of liberated CCA is set to be 1.0% or less. Therefore, even when the consumption of the toner is increased and the surface of the developing roller is thus exposed, the number of the liberated CCA particles is small, thereby reducing adhesion of the liberated CCA to the surface of the developing roller. Even if a few particles of the liberated CCA particles adhere to the surface of the developing roller, the progress of adhering is slower and unevenness of density due to the adhesion of the liberated CCA particles to the surface of the developing roller is not conspicuous because the particle size of the CCA particles is significantly small in comparison to the particle size of the mother particles.
Therefore, good images without unevenness due to the adhesion of the liberated CCA particles to the surface of the developing roller can be obtained over a relatively long period. The toner T of the present invention is particularly advantageous in an apparatus of which a developing device has a pressing means serving the developing roller because, in such an apparatus, adhesion of liberated CCA particles to the developing roller is promoted by the pressing means.
Moreover, if the developing roller has a rough surface, liberated CCA particles are easily caught by the rough surface, thereby promoting the adhesion of the liberated CCA particles to the developing roller. In addition, when the developing roller is conductive, the image force acting on the toner in a direction of making the toner particles to adhere to the developing roller is increased. This means that the conductivity of the developing roller also promotes the adhesion of the liberated CCA particles to the developing roller. Accordingly, the toner of the present invention is extremely effective in a developing device employing a developing roller which is made of metal and is processed by blasting.
Further, according to the toner T of the present invention, the liberation ratio xe2x80x9chxe2x80x9d of liberated pigment particles is set to be 0.6% or less. Because of the small amount of the liberated pigment particles, the probability of contact of liberated pigment particles with the surfaces of processing members such as the developing roller is small, thereby almost preventing the liberated pigment particles from adhering to the surfaces of the processing member including the developing roller. Therefore, the toner T of the present invention can prevent occurrence of white blank in resultant images and reduce the influence of liberated pigment particles on the manifestation of color and permeability as the function of pigment, thus preventing the insufficiency of density, the insufficiency of permeability of OHP, and the like.
Furthermore, according to the toner of the present invention, the liberation ratio xe2x80x9chxe2x80x9d of at least one of a mold releasing agent and a pulverization assisting agent which are liberated from mother particles is set to be 0.4% or less. Because of the small amount of the liberated particles of at least one of the mold releasing agent and the pulverization assisting agent, the probability of contact of liberated particles with the surfaces of processing members such as the developing roller is small, thereby almost preventing the mold releasing agent or the pulverization assisting agent from adhering to the surfaces of the processing member including the developing roller. Therefore, the toner T of this embodiment can prevent occurrence of image defects such as blurs.
Moreover, according to the toner of the present invention, the liberation ratio xe2x80x9chxe2x80x9d of liberated polymerization reaction assisting agent is set to be 0.3% or less so that the amount of liberated polymerization reaction assisting agent is small, thereby making the polymerized toner hard to coagulate and thus improving its fluidity. Therefore, predetermined toner carrying rate can be reliably obtained.
On the other hand, according to the image forming apparatus of the present invention, the aforementioned toner of the present invention is used, thereby preventing liberated additive from adhering to the surfaces of the processing member including the developing roller. Therefore, the image forming apparatus of the present invention can improve the lifetime of the developing device and can provide good images over a long period.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.